Most kids can utter an expletive before they even know their ABCs — probably because their parents (and most other adults) have such terrible pottymouths, according to a new book.

In Holy Sh*t: A Brief History of Swearing, Mellissa Mohr argues that English-speakers actually use a curse word about once every 140 words, the Daily Mail reports.

That makes foul language as popular as first person plural pronouns like "our," "us" and "we." Among the book's findings:

• Cursing usually "kicks off" when a child is 3 or 4.

• About 0.7% of all English words spoken on a given day are swear words.

• The middle class curses less than the wealthy — a Victorian-age habit that "indicates that you are a proper, good person and this is a sign of your morality and awareness of social rules," says Mohr.

• "Aristocrats have a secure position in society, so they can say whatever they want — and may even make a show of doing so," Mohr adds.

• Cursing can be valuable, relieving us of pain (think hammer on finger) or helping us bond with others (like workers complaining about their managers).

• Cursing goes way back: Like us, Romans insulted people with curse words related to sexuality. The most basic of curse words — "sh*t" — dates back to Anglo-Saxons who spoke in Old English.